1. Field of the Invention
The present invention relates to an ignition device for an internal combustion engine, especially an ignition device of an engine having even number cylinders using a differential amplifying circuit.
2. Description of the Prior Arts:
In an internal combustion engine, the engine is highly affected by characteristics of an ignition system especially an ignition timing characteristic of an ignition system. The effectiveness of an engine is decided by the ignition timing characteristics.
However, in the convention ignition device having even number cylinders using a magnet type signal generator and a differential amplifying circuit, the engine is highly affected by variation of waveform to the rotation of the signal output of the magnet type signal generator and the ignition timing characteristics required for the engine has not been given.
Referring to FIGS. 1 to 3, the conventional system will be illustrated.
In FIG. 1, the reference numeral (1) designates a generator coil of a signal generator which is connected in parallel to a serially connected constant voltage diodes (2), (3) in reverse polarity. The output terminals of the col (1) are respectively connected through each resistor (4), (5) to (+), (-) input terminals of a differential amplifying circuit (6). The output terminals of the differential amplifying circuit (6) are respectively connected to each input terminal of an "AND" circuit (7) and a "NAND" circuit (8). The output terminal of the "AND" circuit (7) is connected to a base of a transistor (11). The base and the collector of the transistor (11) are respectively connected through each resistor (9), (10) to a power source (V.sub.B). The emitter of the transistor (11) is grounded. The collector of the transistor (11) is connected to a base of Darlington transistor (12). The emitter of the transistor (12) is grounded and the collector of the transistor (12) is connected through a primary winding (14) of an ignition coil (13) to the power source (V.sub.B). The output terminal of the secondary winding (15) of the ignition coil (13) is connected to a plug of an engine (not shown). The output terminal of the "NAND" circuit (8) is connected to transistors (18), (19) and resistors (16), (17) and an ignition coil (20) in the same manner.
FIG. 2 is a schematic view of the signal generator wherein the reference numeral (25) designates a pick-up comprising the coil (1), a magnet (26) and a core (27) and the reference numeral (28) designates an inductor.
Referring to FIG. 3 of waveforms in operation, the operation of the circuit having said structure will be illustrated.
When a engine is rotated and the output V.sub.o of the generator coil (1) has the waveform shown by the full line in FIG. 3 and the operation level of the differential amplifying circuit (6) comprising the resistors (4), (5) is given as V.sub.s, the output of the A part is shifted to the "H" level at the time t.sub.1 and is shifted to the "L" level at the time t.sub.2. By the operation of the differential amplifying circuit (6), the performances of the "AND" circuit (7) and "NAND" circuit (8) are given as B and C in FIG. 3.
When the output of the differential amplifying circuit (6) is in "H" level, the output of the "AND" circuit (7) is in "H" level and the output of the "NAND" circuit (8) is in "L" level. When the output of the differential amplifying circuit (6) is in "L" level, the output of the "AND" circuit (7) is in "L" level and the output of the "NAND" circuit (8) is in "H" level. The transistor (11) is turned on during the "H" level of the output of the "AND" circuit (7) whereas it is turned off during the "L" level of the output of the "NAND" circuit (8). By the performance, the transistor (12) is operated so as to feed or to break the current shown in FIG. 3 through the primary winding of the ignition coil (13).
When the transistor (11) is turned on, the transistor (12) is turned off to break the current. When the transistor (11) is turned off, the transistor (12) is turned on to feed the current.
A spark voltage shown in FIG. 3F is generated in the secondary winding (15) of the ignition coil (13) during the breaking of the current.
The transistors (18), (19) connected after the "NAND" circuit (8) are performed as the performances of the transistors (11), (12).
These operations are described in the relations of the inputs and the outputs of these circuits.
The spark voltage is applied to the ignition coil (13) at the time t.sub.1 in the positive wave of the output V.sub.o of the dynamo coil (1). The spark voltage is applied to the ignition coil (20) at the time t.sub.2 in the negative wave of the output V.sub.o. When the rotary speed of the engine increases, the output V.sub.o of the generator coil (1) increases to give the waveform shown by the dotted chain line of the output V.sub.o in FIG. 3.
When the positive wave is formed from the initiation facing the projection (a) of the inductor (28) to the core (27) by the rotation of the inductor (28) to the finish, the negative wave is formed from the initiation of departing the projection to the finish. In general, when the magnetic variation angle caused in the relation of the inductor (28) and the core (27) is larger than the rotary angle, the output wave caused in the generator coil is a slack curve. Thus, the output wave of the above-mentioned structure is the slack curve. Therefore, as shown in FIG. 3, the level of the differential amplifying circuit (8) comprising the resistors (4), (5) is V.sub.s. The times t.sub.1 and t.sub.2 for shifting the level of the differential amplifying circuit (6) from "H" to "L" or from "L" to "H" are changed to t.sub.1 ' and t.sub.2 ' by leading for the angle .theta..
In order to decrease the angle .theta., the width of the projection (a) of the inductor (28) is decreased as shown by the dotted line in FIG. 2, the interval of the formation of the positive wave and the negative wave is shorten and a desired ignition interval is not given and the rising of the negative wave is steep but the rising of the positive wave is slack. Thus, the projection shown by the full line of FIG. 2 is used. The spark voltages of the ignition coils (13), (20) are generated in leading for the angle .theta. whereby the ignition time lead for the angle .theta.. The overvoltage output of the dynamo coil (1) is clipped by the constant voltage diodes (2), (3). The ignition timing characteristics of the engine are usually set by a mechanical or electrical system. Thus, the variation of the ignition timing caused by the signal generator adversely affect to the function of the engine. However, when the positive and negative signal output required as the input for the differential amplifying circuit are obtained by one generator coil, the ignition timing is disadvantageously varied by the effect of the output waveform of the generator coil.